Goo.gl is the answer. You can go to the goo.gl website and paste in a link to the web address you want to shorten.
To make things even simpler, you can download the goo.gl shortener Chrome Extension which will show up right next to your Omnibox. Then, all you have to do is be on whatever website you want to share, click the extension, and it will give you the short URL. This short URL is much easier to write up on the board to share with students. (Just be careful with some characters such as a capital i and lowercase l. You can always click the link again to get a different short URL that is easier to read.)
Or, you can get a QR code which you can project or you can copy (Control C) and paste (Control V) it onto a document.
This should help you share links with students and get students to the right spot much quicker.